Rechargeable lithium-ion batteries have revolutionized the portable electronics industry because of their energy density and efficiency. They may also prove valuable for a variety of other applications, including electrification of the transport system and grid-scale stationary energy storage.
However, they suffer from a number of problems, including limited energy and power density, flammability of the liquid organic electrolyte, instability at elevated temperature, short circuits due to lithium dendrites, and decay in energy and power with cycling and long-term storage. Most of these problems are related in some way to the use of unstable liquid or gel organic electrolytes to transfer lithium ions between the electrodes. Replacing this liquid with a solid electrolyte could alleviate these problems.
For instance, the chemical and mechanical stability of the solid electrolyte allows the use of a metallic lithium anode combined with a high-voltage cathode, neither of which is stable in a conventional electrolyte. Such a system would greatly increase the energy and power density compared to a conventional battery (e.g., metallic lithium has a gravimetric capacity that is about 10 times greater than that of graphite). Moreover, the increased energy/power density could greatly reduce material and manufacturing costs since fewer battery cells would be needed for a given application.
Indeed, studies have already demonstrated high-voltage solid-state batteries with less than 10% capacity decay after 10,000 cycles. However, most of the current candidate materials do not transfer lithium ions between the electrodes quickly enough compared to liquid electrolytes. This limits their application to low-power or low-energy thin-film batteries, which are expensive to manufacture and do not provide enough power for electric vehicles. A few material systems have shown promising ionic conductivity, but they suffer from a variety of problems, including electrochemical instability, chemical reactivity with metal oxide cathodes and lithium metal anodes, high cost, complicated fabrication, and high electronic conductivity.